Japanese Patent Laid-Open No. HEI 5-239895 describes a structure in which a photovoltaic apparatus is mounted upon the sheathing of a sloped roof. The photovoltaic apparatus of this reference comprises a plurality of photovoltaic panels which are connected together at their peripheries with sealing joints. The sealing joints are intended to prevent rain water from leaking between the photovoltaic panels. However, because rain water nevertheless often leaks through the joints, weather damage to the underlying roof structure can occur.
Japanese Utility Model Laid-open No. HEI 2-65362 discusses another photovoltaic structure in which photovoltaic panels 2 are mounted on mounting bases 1 in an overlapping fashion on the roof, as shown in FIGS. 1 and 2. Each of the mounting bases 1 has a central groove and step-like portions 1A on both sides of the central groove to support the overlapping photovoltaic panels 2. The step-like portions 1A have receiving electrical connectors 3 to interconnect the photovoltaic panels 2.
In the structure of this photovoltaic apparatus, the photovoltaic panels are partially overlapped like roofing tiles in order to direct rain water over the photovoltaic panels. As a result, the size of each photovoltaic panel is increased to permit them to overlap. In a roofing tile made of a low-priced material, an increase in size does not substantially increase the cost. However, since a photovoltaic panel is typically made of a relatively expensive material, an increase in size can result in a substantially higher cost.
In addition, the photovoltaic panels of this mounting structure are typically installed from the bottom panel up so as to facilitate overlapping the panels. To securely fix the photovoltaic panels on the mounting base, the photovoltaic panels are typically fastened with nails which penetrate through the overlapping portions of the photovoltaic panels. One disadvantage of nail fasteners is that the nails frequently break the photovoltaic panels. In addition, it is often very difficult to replace a broken photovoltaic panel with a new one, because the photovoltaic panels are nailed together in an overlapping structure.
U.S. Pat. No. 4,336,413 describes another photovoltaic apparatus having an overlapping interconnecting structure which, as shown in FIGS. 3 and 4, includes an exterior frame 5 fixed on the periphery of each photovoltaic panel 4. The exterior frame 5 has a downwardly opening groove 5A along the bottom edge of a photovoltaic panel 4, and an upwardly opening groove 5B along the top edge of the photovoltaic panel 4. Further, as shown in FIG. 4, the exterior frame 5 has another upwardly opening groove 5B along one side edge of photovoltaic panel 4, and another downwardly opening groove 5A along the other side edge of photovoltaic panel 4. As shown in FIG. 3, each upwardly opening groove 5B of the panel 4 is received by the downwardly opening groove 5A of an adjacent frame 5 of the adjacent panel. While the structure of this photovoltaic apparatus can reduce the amount of rain water leaking around the boundary between the photovoltaic panels, it is very difficult to replace a broken or damaged photovoltaic panel.
Photovoltaic panels are typically relatively fragile, and as such, are easily damaged. Therefore it would be very advantageous if damaged or broken panel could be readily replaced. For example, breakage can occur when an object blown by a strong wind strikes one or more of the photovoltaic panels. In other instances, tools may be inadvertently dropped on the photovoltaic panels during installation of the photovoltaic panels. Furthermore, people may step on the photovoltaic panels when setting up a TV antenna on the roof. Also, the panels may malfunction, particularly after a prolonged period of time. For example, the photovoltaic panels may not work properly due to degradation of the semiconductor devices in one or more of the photovoltaic panels.
When one photovoltaic panel is broken or malfunctions, the overall output from a photovoltaic apparatus can drop substantially. In a photovoltaic apparatus, the photovoltaic panels are usually connected in series to provide a particular output voltage required for the application. For example, one application may utilize six photovoltaic panels connected in series. If one photovoltaic panel breaks, the output of the entire photovoltaic apparatus can be disabled, even though the other five photovoltaic panels are in good working condition. Therefore, it is very important that a broken or malfunctioning photovoltaic panel in a photovoltaic apparatus be readily replaced with a new one.